Variable displacement pumps require various types of displacement controls dependent upon the usage of the pump. High pressure feedback is almost always a requirement for any variable displacement control. For hydromechanical controls, this feedback is used to actuate a spring loaded spool in either a horsepower or torque limiting control, a high pressure cutoff control, or a load sensing control. Quite often, these controls utilize multiple forms of feedback to perform multiple control functions. When this is the case, the pump controls become very complicated in their design and are often characterized by large hardware configurations. Such large pump controls generally add to the overall cost of the pump.
Some variable displacement pump controls often combine a remotely controllable displacement control with an auxiliary control that utilizes high pressure feedback. Because the remotely controllable displacement control does not utilize high pressure feedback, these combined controls usually require a second bore to perform the auxiliary function. The two bore designs are larger than single bore designs and create additional cost in machining.
Finally, the maximum and minimum displacement settings of the swashplate are often established by contact between the swashplate and mechanical stops. This creates a hard stop which generates excessive noise.
In view of the above, it would be desirable to combine the remotely controllable displacement control with the high pressure feedback in a common bore. In effect, by eliminating the second bore, the overall size and cost of the control would be reduced. It would also be desirable to provide the combination of controls without the use of any double diameters to minimize the potential for concentricity interference. Finally, when the high pressure feedback is used in a torque limiting control, it would be advantageous to provide a maximum hydraulic stop for the pump to reduce the operating noise at maximum flow conditions. It would also be desirable to isolate the high pressure feedback from the displacement control since the displacement control doesn't need high pressure feedback.
The present invention is directed to overcoming one or more of the problems as set forth above.